Aircraft: A319
Phase of flight: Parked
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor

The five of us crew members boarded Aircraft X at ZZZ just as soon as the inbound flight fully deplaned. The inbound flight crew left the APU and APU Bleed ON. Upon stepping aboard and entering the Flight Deck (FD); I noticed an odor that wasn't quite normal. As I was setting up; one of the flight attendants (FAs) called me to the back to check on something. She was standing approximately halfway between first class and the emergency exit row; and as I walked towards her the odor became readily noticeable and more intense. I recognized it as an odor I haven't smelt in many years; that of burning oil coming through the APU driven pack. She asked; 'do you smell that?' which confirmed my thought. I said I certainly did and that we were not going to take this aircraft. She said 'it's that old dirty sock smell' referring to a common term used many years ago (6-8?) pertaining to a period when there were many bad and noxious odors on the Airbus 320 fleet. I told her I agreed and explained it was likely APU oil that was getting into the air conditioning system. I took a few steps further aft and noticed the odor intensified the further back I went. I believe she went to the back of the aircraft to tell another FA as I made my way to the FD to turn the APU Bleed OFF. I briefly explained the situation to the FA in the fwd galley; and told her we were not taking this aircraft. After turning the APU Bleed OFF; I called Maintenance and informed them of the situation. I grabbed the AML and my iPad and headed out to the jetway to fill out the forms. All 3 FAs were now in the jetway and my FO (First Officer) was outside doing his walk-around; preflight inspection. I advised the cleaning crew they should also exit the aircraft; though 2 of them remained aboard as they wanted to finish as they were almost done. The odor dissipated within a few minutes of turning the bleed OFF. I then called my Dispatcher and advised her of the situation; explaining the noxious odor we just experienced; and that some of us already had noticeable symptoms. Per the first items of the online Smoke/Odor/Fume Report in [the] checklist; I asked how everyone was feeling. The 3 FAs and myself had throat irritation; a foul taste in our mouths; and varying degrees of a headache. Mine was slight at that time; hardly worth noting as I began filling out the S/O/F form. My FO had been outside; therefore had minimal exposure and no ill affects. The 4 of them then went up to wait in the terminal while I remained in the jetway to fill out the S/O/F form and AML. A few minutes later; an FA came down to inform me that another FA was feeling light headed and nauseous and that they were contacting their Inflight Coordinator to seek medical assistance. A few minutes later; my FO came down to inform me that FA was now looking faint and had vomited. I gave him the number to Med-Air to give to the FAs. After completing the S/O/F report and making an AML entry; I put the AML back in the FD; shutdown the aircraft and left; intending to go with my FO to another gate (D3?) for a replacement aircraft to complete the flight to ZZZ1. As I was walking up the jetway my symptoms intensified; particularly the headache; and upon entering the terminal it was strongly suggested I have my condition assessed. I called the Chief Pilots [office] to confer and advise them of the situation; then I went with the FAs to [the] hospital. The 4 of us each had POC Blood Gas; arterial tests done; and were monitored. We were discharged shortly after midnight. I contacted an FA to see how she and the rest of the FAs were doing. She reported a new symptom of watery eyes; still with sore throat and headache. Another FA still had a dull headache; and the one who vomited was still not feeling well. The first FA contacted me again later in the day for an update stating no change with her; the other one was now down to a dull headache; and the one suffering the worst now reports body aches. My own symptoms have improved but not yet gone away; still with a mild throat irritation; a nasty taste in my mouth; and almost negligible headache. I have been on the A320 fleet for overall XX years and have experienced many of these events; particularly during that long ago time period when there was a rash of these incidents; many before the cause was determined or rectified. I was rather surprised at how quickly and intensely the symptoms came on during this event. This was by far the most intense experience I've had. As mentioned above; I haven't experienced this in many years. It is my understanding that maintenance procedures had been put in place to prevent these from occurring. I recently read a bulletin message regarding recent events occurring and a new operational procedure to remedy the situation. I am curious as to what may have changed to cause the recent events; as it seemed to me this had been under control. If it is a design flaw it must be fixed. If it is a procedural matter; we must figure out what works for the health and safety of our passengers; and particularly the crew who have potential exposure many times per work day. A319 Captain reported a fume event during preflight that resulted in physiological symptoms in flight and cabin crew members.